218 lines
13 KiB
HTML
218 lines
13 KiB
HTML
<?xml version="1.0" encoding="utf-8"?>
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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
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"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
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<html xmlns="http://www.w3.org/1999/xhtml" lang="en-US" xml:lang="en-us">
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<meta name="dc.date" scheme="iso8601" content="2005-09-19" />
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<meta name="copyright" content="(C) Copyright IBM Corporation 1998, 2006" />
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<meta http-equiv="PICS-Label" content='(PICS-1.1 "http://www.icra.org/ratingsv02.html" l gen true r (cz 1 lz 1 nz 1 oz 1 vz 1) "http://www.rsac.org/ratingsv01.html" l gen true r (n 0 s 0 v 0 l 0) "http://www.classify.org/safesurf/" l gen true r (SS~~000 1))' />
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<meta name="keywords" content="ROLLBACK statement, ROLLBACK, SQL statements,
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unit of work, ending, savepoint, trigger, procedure, WORK clause, HOLD clause" />
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<title>ROLLBACK</title>
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<link rel="stylesheet" type="text/css" href="ibmidwb.css" />
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<link rel="stylesheet" type="text/css" href="ic.css" />
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</head>
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<body>
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<a id="Top_Of_Page" name="Top_Of_Page"></a><!-- Java sync-link -->
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<script language = "Javascript" src = "../rzahg/synch.js" type="text/javascript"></script>
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<a name="rollbac"></a>
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<h2 id="rollbac"><a href="rbafzmst02.htm#ToC_1254">ROLLBACK</a></h2><a id="idx3087" name="idx3087"></a><a id="idx3088" name="idx3088"></a><a id="idx3089" name="idx3089"></a><a id="idx3090" name="idx3090"></a><a id="idx3091" name="idx3091"></a>
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<a name="rolbk"></a>
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<p id="rolbk">The ROLLBACK statement can be used to either:</p>
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<ul>
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<li>End a unit of work and back out all the relational database changes that
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were made by that unit of work. If relational databases are the only recoverable
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resources used by the application process, ROLLBACK also ends the unit of
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work.</li>
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<li>Back out only the changes made after a savepoint was set within the unit
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of work without ending the unit of work. Rolling back to a savepoint enables
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selected changes to be undone.</li></ul>
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<a name="wq1711"></a>
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<h3 id="wq1711"><a href="rbafzmst02.htm#ToC_1255">Invocation</a></h3>
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<p>This statement can be embedded in an application program or issued interactively.
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It is an executable statement that can be dynamically prepared.</p><a id="idx3092" name="idx3092"></a><a id="idx3093" name="idx3093"></a>
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<p>ROLLBACK is not allowed in a trigger if the trigger program
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and the triggering program run under the same commitment definition. ROLLBACK
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is not allowed in a procedure if the procedure is called on a connection
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to a remote application server or if the procedure is defined as ATOMIC. COMMIT is
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not allowed in a function.</p>
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<a name="wq1712"></a>
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<h3 id="wq1712"><a href="rbafzmst02.htm#ToC_1256">Authorization</a></h3>
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<p>None required.</p>
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<a name="wq1713"></a>
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<h3 id="wq1713"><a href="rbafzmst02.htm#ToC_1257">Syntax</a></h3>
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<a href="rbafzmstrollbac.htm#desrolj"><img src="c.gif" alt="Click to skip syntax diagram" /></a>
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<pre class="cgraphic"><span><img src="c.gif" alt="Read syntax diagram" longdesc="rbafzmstsyn375.htm"
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border="0" /></span><a href="#skipsyn-374"><img src="c.gif" alt="Skip visual syntax diagram"
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border="0" /></a> .-WORK-.
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>>-ROLLBACK--+------+--+-----------------------------------+---><
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+-HOLD------------------------------+
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'-TO--SAVEPOINT--+----------------+-'
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'-<span class="italic">savepoint-name</span>-'
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</pre>
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<a name="skipsyn-374" id="skipsyn-374"></a>
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<a name="desrolj"></a>
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<h3 id="desrolj"><a href="rbafzmst02.htm#ToC_1258">Description</a></h3>
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<p>When ROLLBACK is used without the TO SAVEPOINT clause, the unit
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of work in which it is executed is ended. All changes made by SQL schema statements
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and SQL data change statements during the unit of work are backed out. For
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more information see <a href="rbafzmststates.htm#states">Statements</a>.</p>
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<p>The generation of identity values is not under transaction control.
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Values generated and consumed by inserting rows into a table that has an identity
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column are independent of executing the ROLLBACK statement. Also, executing
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the ROLLBACK statement does not affect the IDENTITY_VAL_LOCAL function.</p>
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<p>Special registers are not under transaction control. Executing
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a ROLLBACK statement does not affect special registers.</p>
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<p>Sequences are not under transaction control. Executing a ROLLBACK
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statement does not affect the current value generated and consumed by executing
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a NEXT VALUE expression.</p>
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<p>The impact of ROLLBACK or ROLLBACK TO SAVEPOINT on the contents of a declared
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global temporary table is determined by the setting of the ON ROLLBACK clause
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of the DECLARE GLOBAL TEMPORARY TABLE statement.</p>
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<dl class="parml">
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<dt class="bold">WORK </dt><a id="idx3094" name="idx3094"></a>
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<dd>ROLLBACK WORK has the same effect as ROLLBACK.
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</dd>
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<dt class="bold">HOLD </dt><a id="idx3095" name="idx3095"></a>
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<dd>Specifies a hold on resources. If specified, currently open
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cursors are not closed and all resources acquired during the unit of work,
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except locks on the rows of tables, are held. Locks on specific rows implicitly
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acquired during the unit of work, however, are released.
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<p>At the
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end of a ROLLBACK HOLD, the cursor position is the same as it was at the start
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of the unit of work, unless</p>
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<ul>
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<li>ALWBLK(*ALLREAD) was specified when the program or routine that contains
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the cursor was created</li>
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<li>ALWBLK(*READ) and ALWCPYDTA(*OPTIMIZE) were specified when the program
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or routine that contains the cursor was created</li></ul>
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</dd>
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<dt class="bold">TO SAVEPOINT</dt>
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<dd>Specifies that the unit of work is not to be ended and that only a partial
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rollback (to a savepoint) is to be performed. If a savepoint name is not specified,
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rollback is to the last active savepoint. For example, if in a unit of work,
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savepoints A, B, and C are set in that order and then C is released, ROLLBACK
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TO SAVEPOINT causes a rollback to savepoint B. <span>If no savepoint is active,
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an error is returned.</span>
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<dl class="parml">
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<dt class="bold"><var class="pv">savepoint-name</var></dt>
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<dd>Identifies the savepoint to which to roll back. The name
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must identify a savepoint that exists at the current server.
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</dd>
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</dl>
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<p>After a successful ROLLBACK TO SAVEPOINT, the savepoint continues
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to exist.</p>
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<p>All database changes (including changes made to declared temporary
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tables that were declared with the ON ROLLBACK PRESERVE ROWS clause) that
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were made after the savepoint was set are backed out. All locks and LOB locators
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are retained.</p>
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<p>The impact on cursors resulting from a ROLLBACK TO SAVEPOINT
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depends on the statements within the savepoint:</p>
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<ul>
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<li>If the savepoint contains SQL schema statements on which a cursor is dependent,
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the cursor is closed. Attempts to use such a cursor after a ROLLBACK TO SAVEPOINT
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results in an error.</li>
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<li>Otherwise, the cursor is not affected by the ROLLBACK TO SAVEPOINT (it
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remains open and positioned).</li></ul>
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<p>Any savepoints that are set after the one to which rollback is
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performed are released. The savepoint to which rollback is performed is not
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released.</p>
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</dd>
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</dl>
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<a name="wq1714"></a>
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<h3 id="wq1714"><a href="rbafzmst02.htm#ToC_1259">Notes</a></h3>
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<p><span class="bold">Recommended coding practices:</span> Code an explicit COMMIT
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or ROLLBACK statement at the end of an application process. Either an implicit
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commit or rollback operation will be performed at the end of an application
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process depending on the application environment. Thus, a portable application
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should explicitly execute a COMMIT or ROLLBACK before execution ends in those
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environments where explicit COMMIT or ROLLBACK is permitted.</p>
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<p><span class="bold">Other effects of rollback:</span> Rollback without
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the TO SAVEPOINT clause and HOLD clause causes the following to occur: </p>
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<ul>
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<li>All cursors that were opened during the unit of work are closed.</li>
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<li>All LOB locators, including those that are held, are freed.</li>
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<li>All locks acquired under this unit of work's commitment definition are
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released.</li></ul><p class="indatacontent">ROLLBACK has no effect on the state of connections.</p>
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<p><span class="bold">Implicit ROLLBACK:</span> The ending of the default activation
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group causes an implicit rollback. Thus, an explicit COMMIT or ROLLBACK statement
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should be issued before the end of the default activation group.</p>
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<p>A ROLLBACK is automatically performed when: </p>
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<ol type="1">
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<li>The default activation group ends without a final COMMIT being issued.</li>
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<li>A failure occurs that prevents the activation group from completing its
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work (for example, a power failure).
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<p>If the unit of work is in the prepared
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state because a COMMIT was in progress when the failure occurred, a rollback
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is not performed. Instead, resynchronization of all the connections involved
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in the unit of work will occur. For more information, see the <a href="../rzakj/rzakjcommitkickoff.htm">Commitment control</a> topic.</p></li>
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<li>A failure occurs that causes a loss of the connection to an application server (for
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example, a communications line failure).
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<p>If the unit of work is in the
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prepared state because a COMMIT was in progress when the failure occurred,
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a rollback is not performed. Instead, resynchronization of all the connections
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involved in the unit of work will occur. For more information, see the <a href="../rzakj/rzakjcommitkickoff.htm">Commitment control</a> topic.</p></li>
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<li>An activation group other than the default activation group ends abnormally.</li></ol>
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<p><span class="bold">Row lock limit:</span> A unit of work may include the processing
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of up to and including 4 million rows, including rows retrieved during a SELECT
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INTO or FETCH statement<sup class="fn"><a href="rbafzmstrollbac.htm#fn36">80</a></sup>, and rows inserted, deleted, or
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updated as part of INSERT, DELETE, and UPDATE operations.<sup class="fn"><a id="wq1716" name="wq1716" href="rbafzmstrollbac.htm#wq1717">81</a></sup>
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<p><span class="bold">Unaffected statements:</span> The commit and
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rollback operations do not affect the DROP SCHEMA statement, and this statement
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is not, therefore, allowed if the current isolation level is anything other
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than No Commit (NC).</p>
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<p><span class="bold">ROLLBACK restrictions:</span> A ROLLBACK statement is not
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allowed if commitment control is not active for the activation group. For
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information on determining which commitment definition is used, see the <a href="rbafzmstc4comit.htm#cmtdef">commitment definition</a> discussion in the COMMIT statement.</p>
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<p>ROLLBACK has no effect on the state of connections.</p>
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<p>If, within a unit of work, a CLOSE is followed by a ROLLBACK, all changes
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made within the unit of work are backed out. The CLOSE itself is not backed
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out and the file is not reopened.</p>
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<a name="wq1718"></a>
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<h3 id="wq1718"><a href="rbafzmst02.htm#ToC_1260">Examples</a></h3>
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<p><span class="italic">Example 1:</span> See the <a href="rbafzmstc4comit.htm#commitexamp">Example</a> under
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COMMIT for examples using the ROLLBACK statement.</p>
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<p><span class="italic">Example 2:</span> After a unit of recovery started, assume
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that three savepoints A, B, and C were set and that C was released:</p>
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<pre class="xmp"> <span class="bold">SAVEPOINT</span> A <span class="bold">ON ROLLBACK RETAIN CURSORS</span>;
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...
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<span class="bold">SAVEPOINT</span> B <span class="bold">ON ROLLBACK RETAIN CURSORS</span>;
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....
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<span class="bold">SAVEPOINT</span> C <span class="bold">ON ROLLBACK RETAIN CURSORS</span>;
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...
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<span class="bold">RELEASE SAVEPOINT</span> C</pre>
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<p>Roll back all database changes only to savepoint A:</p>
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<pre class="xmp"> <span class="bold">ROLLBACK WORK TO SAVEPOINT</span> A</pre>
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<p>If a savepoint name was not specified (that is, ROLLBACK WORK
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TO SAVEPOINT), the rollback would be to the last active savepoint that was
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set, which is B.</p><a id="idx3096" name="idx3096"></a><a id="idx3097" name="idx3097"></a>
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<hr /><div class="fnnum"><a id="fn36" name="fn36">80</a>.</div>
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<div class="fntext">Unless you specified COMMIT(*CHG) or COMMIT(*CS), in which case
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these rows are not included in this total.</div><div class="fnnum"><a id="wq1717" name="wq1717" href="rbafzmstrollbac.htm#wq1716">81</a>.</div>
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<div class="fntext">This limit also
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includes: </p>
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<ul>
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<li>Any rows accessed or changed through files opened under commitment control
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through high-level language file processing</li>
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<li>Any rows deleted, updated, or inserted as a result of a trigger or CASCADE,
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SET NULL, or SET DEFAULT referential integrity delete rule.</li></ul></div>
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<br />
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<hr /><br />
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[ <a href="#Top_Of_Page">Top of Page</a> | <a href="rbafzmstrevoket.htm">Previous Page</a> | <a href="rbafzmstsvpt.htm">Next Page</a> | <a href="rbafzmst02.htm#wq1">Contents</a> |
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